This application relates to catalysts and more particularly to homogeneous catalysts for use in polymerization via the ring opening of strained ring systems, and the polymers formed with such catalysts.
As discussed in U.S. Pat No. 5,300,598, in the presence of ring-opening Ziegler catalysts, methylenecyclobutane can be polymerized into a polymer consisting of the structure A, through a ring-opening mechanism. ##STR2##
Polymers having rigid backbones often possess unique properties including high modulus and strength, chirality, and liquid crystallinity which properties lend themselves to use as a structural components or thermoplastic elastomers in structural applications such as fibers, aircraft and automotive parts or in optical devices, such as liquid crystal displays and others. Examples are polyisocyanides, polycarbodiimides, polybenzimidazoles, polyacetylenes, polyimides, and polyamides. The structural stiffness of these polymers is frequently achieved through delocalized .pi. bonding and secondary chemical interactions such as hydrogen bonding. Linear rigid macromolecules consisting solely of saturated hydrocarbon backbones, the rigidity of which derives from .sigma. bond linkages, are virtually unknown, and would represent a new class of isomeric polyolefins. One apparent reason for the paucity lies in the lack of efficient synthetic approaches, since their logical monomeric precursors would necessarily be olefins, which have limited polymerization pathways. However, electrophilic d.sup.0 metallocene centers appear to be highly efficient in a number of carbon-carbon bond transformations.